1991 Ford Bronco Truck Not staying on

Electrical problem
1991 Ford Bronco Engine Size unknown Four Wheel Drive Automatic 400000 miles

I just recently had the fuel pump and filter replaced on my truck but when I drove it after the repairs is was doing a loud skreching sound. I am assunming it is the alternator as every time it starts doing this sound in the past the alternator has died on me. The following day on my way to work the truck starting acting up. It warmed up as usual just fine, the weird thing was that when I turned it on the skreching sound lasted less then a second and then it was quiet-that just seemed troubling to me since in the past it quiet downs as the truck warms up. Every time I stepped on the gas itfelt as if I was forcing it to move. When it finally decided to stop I was able to turn into a residential street where after a couple of minutes of stepping on the gas it was fine but once I let go the truck just turned of. I was able to start it again but it would not stay on. The lights, window, radio and alarm all worked.